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The Mystic Wheel of Contrast

The wheel spins, but the humps and hollows among the wavy spokes stay the same; a hump on one side – is always a hollow on the other. They cannot be real, can they? If the wheel rotates the humps and hollows must rotate too.

The humps and hollows are an illusion. The wavy dark spokes have more white around them where the lines are waviest. A contrast illusion makes them appear slightly less dark in some areas – which makes our brains insist that they are must be 3-dimensional shadows. So we see humps and hollows where none exist. Why we see some as humps and some are hollows is a mystery. It may have something to do with the fact that we almost always assume that a light source must come from above.

Bonus After Effect

If you stare at the center of this illusion for about 20-30 seconds, then look at something else you may see an illusory 'boiling' effect for a moment. Try not to move your eyes as you stare at the wheel. Contrasting black and white colors will excite a patch of your light receptors. The 'boiling' effect is just those receptors relaxing while they replenish with a fresh supply of photochemicals. A purely natural phenomenon.

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